get_upper_ifindexes() iterates over all upper devices and writes their indices into an array without checking bounds. Also the callers assume that the max number of upper devices is MAX_NEST_DEV and allocate excluded_devices[1+MAX_NEST_DEV] on the stack, but that assumption is not correct and the number of upper devices could be larger than MAX_NEST_DEV (e.g., many macvlans), causing a stack-out-of-bounds write. Add a max parameter to get_upper_ifindexes() to avoid the issue. To reproduce, create more than MAX_NEST_DEV(8) macvlans on a device with an XDP program attached using BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS. Then send a packet to the device to trigger the XDP redirect path. Reported-by: syzbot+10cc7f13760b31bd2e61@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/698c4ce3.050a0220.340abe.000b.GAE@google.com/T/ Fixes: aeea1b86f936 ("bpf, devmap: Exclude XDP broadcast to master device") Signed-off-by: Kohei Enju --- Changes: v2: - fix formatting, accounting that max-line-length is 100 v1: https://lore.kernel.org/bpf/20260216201428.65641-1-kohei@enjuk.jp/ --- kernel/bpf/devmap.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c index 2625601de76e..c8c49d86a403 100644 --- a/kernel/bpf/devmap.c +++ b/kernel/bpf/devmap.c @@ -588,16 +588,18 @@ static inline bool is_ifindex_excluded(int *excluded, int num_excluded, int ifin } /* Get ifindex of each upper device. 'indexes' must be able to hold at - * least MAX_NEST_DEV elements. + * least 'max' elements. * Returns the number of ifindexes added. */ -static int get_upper_ifindexes(struct net_device *dev, int *indexes) +static int get_upper_ifindexes(struct net_device *dev, int *indexes, int max) { struct net_device *upper; struct list_head *iter; int n = 0; netdev_for_each_upper_dev_rcu(dev, upper, iter) { + if (n >= max) + break; indexes[n++] = upper->ifindex; } return n; @@ -615,7 +617,8 @@ int dev_map_enqueue_multi(struct xdp_frame *xdpf, struct net_device *dev_rx, int err; if (exclude_ingress) { - num_excluded = get_upper_ifindexes(dev_rx, excluded_devices); + num_excluded = get_upper_ifindexes(dev_rx, excluded_devices, + ARRAY_SIZE(excluded_devices) - 1); excluded_devices[num_excluded++] = dev_rx->ifindex; } @@ -733,7 +736,8 @@ int dev_map_redirect_multi(struct net_device *dev, struct sk_buff *skb, int err; if (exclude_ingress) { - num_excluded = get_upper_ifindexes(dev, excluded_devices); + num_excluded = get_upper_ifindexes(dev, excluded_devices, + ARRAY_SIZE(excluded_devices) - 1); excluded_devices[num_excluded++] = dev->ifindex; } -- 2.51.0